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Re: [Qemu-devel] [PATCH v4 00/21] nbd: add qemu-nbd --list

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v4 00/21] nbd: add qemu-nbd --list
Date: Fri, 18 Jan 2019 10:08:26 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

On 1/17/19 1:36 PM, Eric Blake wrote:
> I got tired of debugging whether a server was advertising the
> correct things during negotiation by inspecting the trace
> logs of qemu-io as client - not to mention that without SOME
> sort of client tracing particular commands, we can't easily
> regression test the server for correct behavior.  The final
> straw was at KVM Forum, when Nir asked me to make sure there
> was a way to easily determine if an NBD server is exposing what
> we really want (and fixing x-dirty-bitmap to behave saner fell
> out as a result of answering that question).
> I note that upstream NBD has 'nbd-client -l $host' for querying
> just export names (with no quoting, so you have to know that
> a blank line means the default export), but it wasn't powerful
> enough, so I implemented 'qemu-nbd -L' to document everything.
> Upstream NBD has separate 'nbd-client' and 'nbd-server' binaries,
> while we only have 'qemu-nbd' (which is normally just a server,
> but 'qemu-nbd -c' also operates a second thread as a client).
> Our other uses of qemu as NBD client are for consuming a block
> device (as in qemu-io, qemu-img, or a drive to qemu) - but those
> binaries are less suited to something so specific to the NBD
> protocol.
> Bonus: As a result of my work on this series, nbdkit now supports
> NBD_OPT_INFO (my interoperability testing between server
> implementations has been paying off, both at fixing server bugs,
> and at making this code more reliable across difference in valid
> servers).
> Also available at:
> https://repo.or.cz/qemu/ericb.git qemu-nbd-list-v4

Vladimir spotted a few more tweaks to make, but they all look
sufficiently minor that I'll go ahead and queue this on my NBD tree for
a pull request on Monday, rather than posting a v5, if there aren't any
other major comments in the meantime.

Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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